The desire for identifying and quantifying the constituents of contaminants in gases has generated a wide variety of detection means for testing various gases. The particular method or apparatus employed for determining the contaminants present in a given gas is often determined by the availability or condition of the particular sample which is to be interrogated. For example, concern about the release of hazardous substances into the environment, specifically the earth's atmosphere, has created a need for apparatus or methods for detecting for the presence of such hazardous substances as contaminants in a sample of air from the atmosphere.
A variety of apparatus or methods are known in the art for testing to determine whether the atmosphere contains contaminants. These apparatus and methods can be used to confirm or refute a suspected release of a given hazardous substance or contaminant. One example of such apparatus or methodology for testing air samples from the atmosphere begins with drawing a volume of atmospheric air through a filter, typically constructed of paper. After a predetermined volume of air has passed through the filter, the filter may then be interrogated by a wide variety of means to determine the presence of a contaminant. A variety of tradeoffs are apparent in the design of apparatus for the use of filters in air sampling. For example, a particular filter has a specific permeability per unit of surface area to a particular gas, such as air, at a certain pressure drop across the filter. Testing for very small amounts or trace contaminants generally requires a large volume of air to be passed through the filter to collect a detectable amount of contaminant for interrogation. Thus, to pass a sufficient volume of gas through a section of the particular filter requires a sufficient surface area of the filter, a sufficient pressure drop across the filter, and sufficient time to allow the required volume of gas to pass through the filter. A reduction in any of these variables requires a corresponding increase in one of the others to capture the same amount of contaminant on the filter.
If, for example, power available for use by the detection apparatus is limited, a smaller pump is necessary which will decrease the pressure drop across the filter. To collect contaminant samples under such conditions, which are identical to the contaminant samples collected with a larger pump, will thus require either a longer period of time for sample collection, or a larger cross section of filter paper, or some combination of the two. Restrictions of other operating parameters may force similar tradeoffs between the variables including the type of filter utilized, the surface area of the filter through which the gas is passed, the pressure drop across the filter, and the time allowed for the required volume of gas to pass through the filter.
The particular interrogation means utilized will be dependent upon the particular contaminant of interest. For example, interrogating a filter for contaminant radionuclides may be accomplished with a germanium detector or a sodium iodide detector. Interrogating a filter for non-radioactive inorganic contaminants may be accomplished with an x-ray fluorescence detector.
The effectiveness or accuracy of such interrogation methods is dependent upon the physical proximity of the detection means to the contaminant to be detected. For example, the sensitivity of a germanium detector interrogating a sample for the presence of radionuclides is inversely proportional to the distance between the radionuclide and the germanium detector. Also, should a particular sample contain a very small amount of the contaminant of interest spread across the surface area of the filter, the effectiveness and accuracy of many such interrogation methods may require that the entire mass of a contaminant sample be interrogated simultaneously. For both of these reasons, it is often advantageous to consolidate or minimize the surface area of the filter prior to interrogation and to cause the entire surface area of the filter to be interrogated simultaneously by insuring that the entire surface area of the filter is in close proximity to the detection means.
Minimization of the surface area of the filter for effective interrogation conflicts with maximization of the surface area of the filter for contaminant collection. Those skilled in the art have overcome these seemingly contradictory goals by using large surface area filters during sample collection and then subsequently manually folding the filter over on itself, or manually packing the filter into a small volume, prior to interrogation. Prior to the present invention, there has been no effective method known in the art for automatically consolidating the filter for interrogation.
Thus, there exists a need among those skilled in the art for an apparatus which automatically consolidates a filter utilized in a gas sampling apparatus prior to interrogation.